Can an heir to an estate, in canada, be held responsible for unpaid taxes?

Answer 1

Not sure about Canada.
Most places, the Estate is responsible for personal taxes.
If there is a transfer of real estate involved, the tax burden on the land, (real estate taxes), may well follow with the land if the estate doesn't settle them before transfer, as is normally done.
If the taxes exceed the available cash, the taxes will follow the land or a forced sale may result.

Answer 2

I can only answer for US, the estate is responsible for unpaid taxes.